From PathfinderWiki
The GameMastery line logo

The GameMastery line of products from Paizo Inc. provided tools to help busy tabletop roleplaying Game Masters prepare for adventures. Many of the GameMastery lines were later rebranded as Pathfinder product lines, including the GameMastery Cards, Flip-Mat, Map Pack, and Modules lines.

Product lines

The standalone GameMastery Guide is also considered part of the core Pathfinder Roleplaying Game line.